Actuator

Abstract

An actuator arranged to be movable between an extended condition and a compressed condition and being biased to an intermediate condition between and distinct from the extended condition and the compressed condition. The actuator includes a damping device arranged to define the damping coefficient of the actuator. The damping device is arranged to provide a relatively low damping coefficient when the actuator is in a first condition distinct from the intermediate condition, and a relatively high damping coefficient when the actuator is in a second condition, the second condition being distinct from the first condition and being equal or adjacent to the intermediate condition

The invention claimed is: 
     
       1. A centre seeking actuator arranged to be movable between an extended condition and a compressed condition and being biased to an intermediate condition between and distinct from the extended condition and the compressed condition, the centre seeking actuator comprising:
 A casing defining an inner volume having a first end and a second end; 
 A floating piston slidably disposed in the inner volume of the casing so as to be movable relative to the casing; 
 a piston rod slidably disposed within the floating piston; 
 a pressurised fluid within the inner volume, the pressurized fluid acting on respective surfaces of the floating piston and the piston rod to generate a force to move the floating piston towards the first end and move the piston rod towards the second end to cause the centre seeking actuator to assume the intermediate condition; and 
 a damping device arranged to define the damping coefficient of the actuator, the damping device being arranged to provide a relatively low damping coefficient when the actuator is in a first condition distinct from the intermediate condition, and a relatively high damping coefficient when the actuator is in a second condition, the second condition being distinct from the first condition and being equal or adjacent to the intermediate condition wherein the damping device comprises a space between the piston rod and the floating piston. 
 
     
     
       2. The centre seeking actuator according to  claim 1 , wherein the second condition is closer to the intermediate condition than to the extended condition or the compressed condition. 
     
     
       3. The centre seeking actuator according to  claim 1 , wherein the damping device is arranged to increase and/or decrease the damping coefficient by a factor of at least a factor of two between the first condition and the second condition. 
     
     
       4. The centre seeking actuator according to  claim 1 , wherein the damping device is arranged to provide a plurality of second conditions each with a relatively high damping coefficient. 
     
     
       5. The centre seeking actuator according to  claim 1 , wherein the damping device is arranged to vary the damping coefficient in accordance with the extension state of the actuator. 
     
     
       6. The centre seeking actuator according to  claim 1 , wherein the damping device is a passive device. 
     
     
       7. The centre seeking actuator according to  claim 1 , wherein the actuator is biased towards the intermediate condition from both the contracted and extended conditions. 
     
     
       8. The centre seeking actuator according to  claim 1 , wherein the actuator is arranged to be driven by a fluid. 
     
     
       9. The centre seeking actuator according to  claim 1  including:
 a first hydraulic chamber; 
 a second hydraulic chamber; and 
 a fluid flow path providing fluid communication between the first hydraulic chamber and the second hydraulic chamber, 
 wherein the damping device comprises a fluid flow restriction device arranged to modify the damping co-efficient of the actuator by varying the fluid diameter of the fluid flow path. 
 
     
     
       10. The centre seeking actuator according to  claim 9 , wherein the fluid flow restriction device comprises an elongate bar arranged to move axially within an aperture or orifice of fixed size, the bar including a region of reduced cross-section midway along the bar. 
     
     
       11. The centre seeking actuator according to  claim 10 , wherein the cross section of the bar or pin varies along a portion or portions of its length. 
     
     
       12. The centre seeking actuator according to  claim 1 , wherein:
 the floating piston comprises an elongate pin; 
 the piston rod has a piston rod aperture surrounding the elongate pin; and 
 the elongate pin includes an engagement formation arranged to engage the piston rod at a predetermined degree of relative separation to inhibit further separation of the floating piston and the piston rod. 
 
     
     
       13. The centre seeking actuator according to  claim 12 , wherein the elongate pin comprises a metering pin having a cross-sectional profile that varies along the length of the metering pin. 
     
     
       14. The centre seeking actuator of according to  claim 13 , wherein the metering pin has a first cross-sectional area at a first location at which the piston rod aperture is positioned when the actuator is in the intermediate condition, and a second cross-sectional area at a second location at which the piston rod aperture is positioned when the actuator is in the first condition. 
     
     
       15. An assembly including a centre seeking actuator according to  claim 1  arranged to bias a first part of the assembly to assume a predetermined position relative to a second part of the assembly, the assembly being arranged, in use, to force the actuator to assume the first condition when in a first state and having a second state in which the actuator moves the first part of the assembly to assume the predetermined position relative to the second part of the assembly. 
     
     
       16. The assembly according to  claim 15 , wherein the assembly comprises an aircraft landing gear assembly. 
     
     
       17. The assembly according to  claim 16 , wherein the first part of the assembly comprises a bogie beam and the second part of the assembly comprises another component of the landing gear assembly. 
     
     
       18. The centre seeking actuator according to  claim 1 , wherein the centre seeking actuator is configured such that internal fluid pressure can overcome an applied external compression force to return to the intermediate position from the compressed condition and can overcome an applied extension force to return to the intermediate position from the extended condition. 
     
     
       19. The centre seeking actuator according to  claim 1 , wherein internal fluid pressure can overcome external compression or extension forces to force the centre seeking actuator to move to the intermediate condition and remain in the intermediate condition. 
     
     
       20. The centre seeking actuator according to  claim 1 , wherein the centre seeking actuator is biased to the intermediate condition from the extended condition and from the compressed condition. 
     
     
       21. A centre seeking actuator comprising:
 a first coupling formation for coupling the centre seeking actuator to a first structure distinct from the centre seeking actuator; 
 a second coupling formation for coupling the centre seeking actuator to a second structure distinct from the centre seeking actuator; 
 wherein the centre seeking actuator is configured to be movable between an extended condition in which the first and second coupling formations are relatively far from one another and a compressed condition in which the first and second coupling formations are relatively close to one another, the centre seeking actuator being biased by internal fluid pressure to an intermediate condition between and distinct from the extended condition and the compressed condition, the internal fluid pressure being sufficient to overcome an external compression force applied between the first and second couplings to return the centre seeking actuator to the intermediate condition from the compressed condition and the internal fluid pressure being sufficient to overcome an external extension force applied between the first and second couplings to return the centre seeking actuator to the intermediate condition from the extended condition; and 
 the centre seeking actuator further comprising a damping device arranged to define a damping coefficient of the actuator, the damping device being configured to provide a relatively low damping coefficient when the actuator is in a first condition distinct from the intermediate condition, and a relatively high damping coefficient when the actuator is in a second condition, the second condition being distinct from the first condition and being equal or adjacent to the intermediate condition the centre seeking actuator further comprising: a casing defining an inner volume; a floating piston slidably disposed in the inner volume of the casing so as to be movable relative to the casing; a piston rod slidably disposed within the floating piston; wherein the damping device comprises a space between the piston rod and the floating piston.